Color emissive displays, such as cathode ray tubes and liquid crystal displays, typically comprise an array of red, green, and blue (RGB) pixels. By carefully controlling the ratio and intensity of the colored pixels it is possible to produce a huge gamut of colors. For example, a display having only red, green, and blue pixels can achieve so called “true color” with only 256 gray levels per pixel (8 bits per pixel, a.k.a. 24-bit RGB). Because this “true color” gamut includes over 16 million different color combinations, it is possible to reproduce nearly all of the colors that are perceived by the human eye in such a display. Accordingly, most digital images and video are now produced, saved, and shared in an RGB format that assumes 256 different shades for each RGB subpixel.
In the current state of the art, there exist several embodiments of color reflective displays that differ in their mechanism of producing color. Although such displays are capable of rendering multiple colors at every pixel location (for example, white, the three subtractive primary colors (cyan, magenta and yellow) and the three additive primary colors (red, green and blue), in the current state of the art they are not capable of rendering colors corresponding to 256 RGB levels at every pixel location. This is in contrast to a typical emissive display (such as a liquid crystal display or a display made using light-emitting diodes) that is capable of providing at least 256 different intensity levels in red, green and blue channels, for a total of 224 different colors, at each pixel location.
When modern image data is transferred to a display platform that has lesser color capabilities, the colors in the image data must be mapped to the new color palette. For example, as shown in FIG. 1, the display platform may include a pixel (black box) including only a red, a white, a blue, and a green subpixel. For RGB→RGBW transformations, the easiest way to transform high-color-density RGB data is to compensate for the total color depth in the red, green, and blue pixels by increasing or decreasing the intensity of the white pixel, as shown in FIG. 2. This technique is known to produce satisfying colors, especially when each of the RGBW subpixels has more than two optical states. Greater details of this process can be found in U.S. Pat. No. 5,929,843, which is incorporated herein by reference in its entirety.
Nonetheless, some displays only provide two states for each pixel, i.e., “on” and “off,” sometimes referred to as 1-bit per channel. When transforming modern color image data for a 1-bit RGBW display, the above process of compensating for the total color depth with the white pixel is unsatisfactory. In particular, the transformation illustrated in FIG. 2 results in only eight colors: black, white, red, green, blue, cyan, magenta, and yellow. This limited palette results in “washed out” images that are not pleasing to a viewer. Accordingly, there is need for an improved method for mapping modern image data for presentation on a display having RGBW subpixels, wherein each subpixel has only an “on” and an “off” state.